The Transmission Control Protocol (TCP) has successfully governed the Internet congestion control for two decades. It is by now, however, widely recognized that TCP has started to reach its limits and that new congestion control protocols are needed in the near future. This has spurred an intensive research effort searching for new congestion control designs that meet the demands of a future Internet scaled up in size, capacity and heterogeneity. In this thesis we derive network fluid flow models suitable for analysis and synthesis of window based congestion control protocols such as TCP. In window based congestion control the transmission rate of a sender is regulated by: (1) the adjustment of the so called window, which is an upper bound on the number of packets that are allowed to be sent before receiving an acknowledgment packet (ACK) from the receiver side, and (2) the rate of the returning ACKs. From a dynamical perspective, this constitutes a cascaded control structure with an outer and an inner loop. The first contribution of this thesis is a novel dynamical characterization and an analysis of the inner loop, generic to all window based schemes and formed by the interaction between the, so called, ACK-clocking mechanism and the network. The model is based on a fundamental integral equation relating the instantaneous flow rate and the window dynamics. It is verified in simulations and testbed experiments that the model accurately predicts dynamical behavior in terms of system stability, previously unknown oscillatory behavior and even fast phenomenon such as traffic burstiness patterns present in the system. It is demonstrated that this model is more accurate than many of the existing models in the literature. In the second contribution we consider the outer loop and present a detailed fluid model of a generic window based congestion control protocol using queuing delay as congestion notification. The model accounts for the relations between the actual packets in flight and the window size, the window control, the estimator dynamics as well as sampling effects that may be present in an end-to-end congestion control algorithm. The framework facilitates modeling of a quite large class of protocols. The third contribution is a closed loop analysis of the recently proposed congestion control protocol FAST TCP. This contribution also serves as a demonstration of the developed modeling framework. It is shown and verified in experiments that the delay configuration is critical to the stability of the system. A conclusion from the analysis is that the gain of the ACK-clocking mechanism dramatically increases with the delay heterogeneity for the case of an equal resource allocation policy. Since this strongly affects the stability properties of the system, this is alarming for all window based congestion control protocols striving towards proportional fairness. While these results are interesting as such, perhaps the most important contribution is the developed stability analysis technique. / QC 20100813

Intentional amendment of soil with charcoal (called biochar) is a promising new approach to sequester atmospheric carbon dioxide and increase soil fertility. However, the environmental properties of biochars can vary with production conditions, making it challenging to engineer biochars that are simultaneously optimized for carbon sequestration, nutrient storage, and water-holding capacity. For this reason, I have undertaken a systematic study to (a) determine the pyrolysis conditions that lead to biochars with desired chemical and physical properties, and (b) find how these properties affect the water-holding capacity and nutrient adsorption in biochar-soil mixtures. First, a library of biochars was produced in a custom-built pyrolysis reactor under precisely controlled conditions. The chemical and physical structures of the produced biochars were characterized with various analytical techniques including 13C NMR, XPS, EA and BET pore surface analysis. My results suggest that the chemical composition and pore structure of biochars are determined not just by the maximum heat treatment temperature, but also by several other factors that include the pyrolysis heating rate, treatment time at the maximum temperature and particle size. I also tested a new approach that combines thermogravimetric reactivity measurements, diffusion-reaction theory and structural models to achieve a better characterization of the complicated multi-scale pore structure of biochars. The structural models treat biochars as porous solids having micro- and macropores of different shapes and exhibiting widely ranging pore-size distributions. Simulations results are then compared to experimental data to identify the presence of ordered or random pore networks and test their size distributions and connectivity. I then developed a multi-solid one-dimensional model that can use experimentally determined biochar properties to predict their field performance in beds packed with soil/biochar mixtures. The model used a system of coupled partial differential equations to describe the dynamic adsorption/elution of ammonium nitrate, a model fertilizer, in columns packed with biochar/soil mixtures and perfused with aqueous solutions of the fertilizer. The PDE system was solved using orthogonal collocation on finite elements. My chromatographic model accounted for all the important processes occurring in this system, including external mass transfer between the fluid phase and the solid particles, as well as intraparticle diffusion and adsorption of the solute on the pore surface area of the sorbents. To our knowledge, this is the first chromatographic model that accounted explicitly for the presence of two solid phases with widely different pore structures and adsorption capacities. A systematic parametric study was carried out to determine the importance of each system parameter. The adsorption equilibrium parameters and the intraparticle effective diffusivity of ammonium had the most significant effect on environmental performance. To complete the theoretical analysis, I also developed a model to describe the saturation and drainage of water from the packed column. The model accounted for all the important processes occurring in this system: (a) water exchange between the interstitial pore region and two different smaller pore regions and (b) water flow inside the larger pore region and the two different smaller pore regions. The transient mass balances led to a system of partial differential equations that was solved using block centered finite difference.

In this study, an entropy generation minimization procedure is employed to optimize the overall performance (thermal and hydrodynamic) of isolated fin geometries and pin-fin heat sinks. This allows the combined effects of thermal resistance and pressure drop to be assessed simultaneously as the heat sink interacts with the surrounding flow field. New general expressions for the entropy generation rate are developed using mass, energy, and entropy balances over an appropriate control volume. The formulation for the dimensionless entropy generation rate is obtained in terms of fin geometry, longitudinal and transverse pitches, pin-fin aspect ratio, thermal conductivity, arrangement of pin-fins, Reynolds and Prandtl numbers. It is shown that the entropy generation rate depends on two main performance parameters, i. e. , thermal resistance and the pressure drop, which in turn depend on the average heat transfer and friction coefficients. These coefficients can be taken from fluid flow and heat transfer models. An extensive literature survey reveals that no comprehensive analytical model for any one of them exists that can be used for a wide range of Reynolds number, Prandtl number, longitudinal and transverse pitches, and thermal conductivity. This study is one of the first attempts to develop analytical models for the fluid flow and heat transfer from single pins (circular and elliptical) with and without blockage as well as pin-fin arrays (in-line and staggered). These models can be used for the entire laminar flow range, longitudinal and transverse pitches, any material (from plastic composites to copper), and any fluid having Prandtl numbers (≥0. 71). In developing these models, it is assumed that the flow is steady, laminar, and fully developed. Furthermore, the heat sink is fully shrouded and the thermophysical properties are taken to be temperature independent. Using an energy balance over the same control volume, the average heat transfer coefficient for the heat sink is also developed, which is a function of the heat sink material, fluid properties, fin geometry, pin-fin arrangement, and longitudinal and transverse pitches. The hydrodynamic and thermal analyses of both in-line and staggered pin-fin heat sinks are performed using parametric variation of each design variable including pin diameter, pin height, approach velocity, number of pin-fins, and thermal conductivity of the material. The present analytical results for single pins (circular and elliptical) and pin-fin-arrays are in good agreement with the existing experimental/numerical data obtained by other investigators. It is shown that the present models of heat transfer and pressure drop can be applied for a wide range of Reynolds and Prandtl numbers, longitudinal and transverse pitches, aspect ratios, and thermal conductivity. Furthermore, selected numerical simulations for a single circular cylinder and in-line pin-fin heat sink are also carried out to validate the present analytical models. Results of present numerical simulations are also found to be in good agreement.

Internet protocol TV (IPTV) is predicted to be the key technology winner in the future. Efforts to accelerate the deployment of IPTV centralized model which is combined of VHO, encoders, controller, access network and Home network. Regardless of whether the network is delivering live TV, VOD, or Time-shift TV, all content and network traffic resulting from subscriber requests must traverse the entire network from the super-headend all the way to each subscriber's Set-Top Box (STB).IPTV services require very stringent QoS guarantees When IPTV traffic shares the network resources with other traffic like data and voice, how to ensure their QoS and efficiently utilize the network resources is a key and challenging issue. For QoS measured in the network-centric terms of delay jitter, packet losses and bounds on delay. The main focus of this thesis is on the optimized bandwidth allocation and smooth datatransmission. The proposed traffic model for smooth delivering video service IPTV network with its QoS performance evaluation. According to Maglaris et al [5] First, analyze the coding bit rate of a single video source. Various statistical quantities are derived from bit rate data collected with a conditional replenishment inter frame coding scheme. Two correlated Markov process models (one in discrete time and one incontinuous time) are shown to fit the experimental data and are used to model the input rates of several independent sources into a statistical multiplexer. Preventive control mechanism which is to be include CAC, traffic policing used for traffic control.QoS has been evaluated of common bandwidth scheduler( FIFO) by use fluid models with Markovian queuing method and analysis the result by using simulator andanalytically, Which is measured the performance of the packet loss, overflow and mean waiting time among the network users.

Internet protocol TV (IPTV) is predicted to be the key technology winner in the future. Efforts to accelerate the deployment of IPTV centralized model which is combined of VHO, encoders, controller, access network and Home network. Regardless of whether the network is delivering live TV, VOD, or Time-shift TV, all content and network traffic resulting from subscriber requests must traverse the entire network from the super-headend all the way to each subscriber's Set-Top Box (STB). IPTV services require very stringent QoS guarantees When IPTV traffic shares the network resources with other traffic like data and voice, how to ensure their QoS and efficiently utilize the network resources is a key and challenging issue. For QoS measured in the network-centric terms of delay jitter, packet losses and bounds on delay. The main focus of this thesis is on the optimized bandwidth allocation and smooth data transmission. The proposed traffic model for smooth delivering video service IPTV network with its QoS performance evaluation. According to Maglaris et al [5] first, analyze the coding bit rate of a single video source. Various statistical quantities are derived from bit rate data collected with a conditional replenishment inter frame coding scheme. Two correlated Markov process models (one in discrete time and one in continuous time) are shown to fit the experimental data and are used to model the input rates of several independent sources into a statistical multiplexer. Preventive control mechanism which is to be including CAC, traffic policing used for traffic control. QoS has been evaluated of common bandwidth scheduler( FIFO) by use fluid models with Markovian queuing method and analysis the result by using simulator and analytically, Which is measured the performance of the packet loss, overflow and mean waiting time among the network users.

In this study, an entropy generation minimization procedure is employed to optimize the overall performance (thermal and hydrodynamic) of isolated fin geometries and pin-fin heat sinks. This allows the combined effects of thermal resistance and pressure drop to be assessed simultaneously as the heat sink interacts with the surrounding flow field. New general expressions for the entropy generation rate are developed using mass, energy, and entropy balances over an appropriate control volume. The formulation for the dimensionless entropy generation rate is obtained in terms of fin geometry, longitudinal and transverse pitches, pin-fin aspect ratio, thermal conductivity, arrangement of pin-fins, Reynolds and Prandtl numbers. It is shown that the entropy generation rate depends on two main performance parameters, i. e. , thermal resistance and the pressure drop, which in turn depend on the average heat transfer and friction coefficients. These coefficients can be taken from fluid flow and heat transfer models. An extensive literature survey reveals that no comprehensive analytical model for any one of them exists that can be used for a wide range of Reynolds number, Prandtl number, longitudinal and transverse pitches, and thermal conductivity. This study is one of the first attempts to develop analytical models for the fluid flow and heat transfer from single pins (circular and elliptical) with and without blockage as well as pin-fin arrays (in-line and staggered). These models can be used for the entire laminar flow range, longitudinal and transverse pitches, any material (from plastic composites to copper), and any fluid having Prandtl numbers (≥0. 71). In developing these models, it is assumed that the flow is steady, laminar, and fully developed. Furthermore, the heat sink is fully shrouded and the thermophysical properties are taken to be temperature independent. Using an energy balance over the same control volume, the average heat transfer coefficient for the heat sink is also developed, which is a function of the heat sink material, fluid properties, fin geometry, pin-fin arrangement, and longitudinal and transverse pitches. The hydrodynamic and thermal analyses of both in-line and staggered pin-fin heat sinks are performed using parametric variation of each design variable including pin diameter, pin height, approach velocity, number of pin-fins, and thermal conductivity of the material. The present analytical results for single pins (circular and elliptical) and pin-fin-arrays are in good agreement with the existing experimental/numerical data obtained by other investigators. It is shown that the present models of heat transfer and pressure drop can be applied for a wide range of Reynolds and Prandtl numbers, longitudinal and transverse pitches, aspect ratios, and thermal conductivity. Furthermore, selected numerical simulations for a single circular cylinder and in-line pin-fin heat sink are also carried out to validate the present analytical models. Results of present numerical simulations are also found to be in good agreement.

Orifices are essential devices for measurement and control of flow. It is important to define the flow field and understand the flow characteristics behind an orifice for the sake of reliability measures in many hydraulic engineering applications. Since analytical and experimental solutions are restricted, a numerical solution is obtained using volume of fluid (VOF) method with the CFD solver, FLUENT, for sharp crested orifices, orifice tubes and slots. The results are compared to the available data in the literature / also a large spectrum of data collection has been achieved.

The infiltration of water in asphalt pavements promotes moisture damage primarily through damaging the binder cohesive bond and the adhesive bond between aggregates and binder. Moisture damage is associated with excessive deflection, cracking, and rutting. The first step in addressing the problems caused by the presence of water within pavement systems is quantifying the permeability of hot mix asphalt (HMA) mixes. This dissertation deals with the development of empirical-analytical and numerical approaches for predicting the permeability of HMA. Both approaches rely on the analysis of air void distribution within the HMA microstructure. The empirical-analytical approach relies on the development of modified forms of the Kozeny-Carman equation and determining the material properties involved in this equation through three dimensional microstructure analyses of X-ray Computed Tomography (CT) images. These properties include connected percent air voids (effective porosity), tortuosity, and air void specific surface area. A database of materials and permeability measurements was used to verify the developed predicting equation. The numerical approach, which is the main focus of this study, includes the development of a finite difference numerical simulation model to simulate the steady incompressible fluid flow in HMA. The model uses the non-staggered system that utilizes only one cell to solve for all governing equations, and it is applicable for cell Reynolds number (Rec) values that are not restricted by |Rec|≤2. The validity of the numerical model is verified through comparisons with closed-form solutions for idealized microstructure. The numerical model was used to find the components of the three-dimensional (3-D) permeability tensor and permeability anisotropy values for different types of HMA mixes. It was found that the principal permeability directions values are almost in the horizontal and vertical directions with the maximum permeability being in the horizontal direction.

Seafloor hydrothermal systems play a key role in Earth fs energy and geochemical budgets. They also support the existence and development of complex chemosynthetic biological ecosystems that use the mineral-laden fluids as a source of energy and nutrients. This dissertation focuses on two inter-related topics: (1) heat output and geochemical fluxes at mid-ocean ridges, and (2) structural deformation of oceanic lithosphere related to subsurface serpentinization in submarine settings. The determination of heat output is important for several reasons. It provides important constraints on the physics of seafloor hydrothermal processes, on the nature of the heat sources at mid-ocean ridges, and on nutrient transport to biological ecosystems. Despite its importance, measurements of hydrothermal heat outputs are still scarce and cover less than 5% of active hydrothermal vent sites. In this work, we report development of two new devices designed to measure fluid flow velocities from the submersible at temperatures of up to 450 C and depths 5,000 m. By using these instruments on 24 Alvin dives, new measurements of hydrothermal heat output have been conducted at the Juan de Fuca Ridge, including first measurements from the High Rise and Mothra hydrothermal fields. The collected data suggest that the high-temperature heat output at the Main Endeavour Field (MEF) may be declining since the 1999 eruption. The flow measurement results, coupled with in-situ geochemical measurements, yielded the first estimates of geochemical fluxes of volatile compounds at MEF and Mothra. Our findings indicate that geochemical flux from diffuse flows may constitute approximately half of the net geochemical flux from Juan de Fuca Ridge. It has recently been recognized that serpentinization of mantle peridotites, due to its exothermic nature, may be a mechanism contributing to the heat output at mid-ocean ridges. The tectonic response of the crust to serpentinization of extensively distributed peridotites at mid-ocean ridges and subduction zones could provide a means of characterizing serpentinized regions in the oceanic lithosphere. These regions are often associated with surface topographic anomalies that may result from the volume expansion caused by the serpentinization reactions. Although there is a clear correlation between tectonics and serpentinization, the link is complex and still not understood. In this dissertation, we calculated the transformation strain and surface uplift associated with subsurface serpentinization of variously shaped ultramafic inclusions. Application of the results to explain the anomalous topographic salient at the TAG hydrothermal field (Mid-Atlantic Ridge) suggests that this feature may result from a serpentinized body beneath the footwall of a detachment fault. Because the depth of the potential serpentinized region appears to be more than 1.5 times the size of the inclusion, the uplift profile is relatively insensitive to the exact location or shape of the serpentinized domain. The rate of exothermic heat release needed to produce the serpentinized volume may contribute to the ongoing diffuse flow. Application of the results to an uplift feature associated with the Kyushu ]Palau subduction zone in the western Pacific, shows that approximately 3% transformational strain in an inclined serpentinized region of the mantle wedge near the subducted Kyushu ]Palau Ridge may result in the observed uplift on the Miyazaki Plain. Using the uplift data may help to constrain the level of the subsurface serpentinization.

<p>The effects of different shearing processes and sample sizes on the fluid flow anisotropy and its impact on particle transport process in rough rock fractures are significant factors that need to be considered in the performance and safety assessments of underground nuclear waste repositories. The subjects, however, have not been adequately investigated previously in either laboratory experiments or numerical modeling. This thesis addresses these problems using numerical modeling approaches.</p><p>The modeling consists of two parts: 1) fluid flow simulations considering more complex but realistic flow boundary conditions during shear processes that cannot be realized readily in laboratory experiments, using digitalized fracture surfaces scanned in the laboratory, so that anisotropic fluid flow induced by shearing with channeling phenomenon can be directly simulated and quantified; 2) particle tracking simulations to demonstrate the impacts of such channeling effects on characteristic properties of particle transport. The numerical method chosen for the simulations is the Finite Element Method (FEM). Scale effects were considered in the simulations by using fracture surface samples of different sizes.</p><p>The distributions of fracture aperture during shear were obtained by numerically generating relative translational and rotary movements between two digitalized surfaces of a rock fracture replica without considering normal loading. From the evolutions of the aperture distributions during the shearing processes, the evolutions of the transmissivity fields were determined by assuming the validity of the cubic law locally. A geostatistical approach was used to quantify the scale effects of the aperture and transmissivity fields. The fluid flow was simulated using different flow boundary conditions, corresponding to translational and rotary shear processes. Corresponding to translational shear (with a 1 mm shear displacement interval up to a maximum shear displacement of 20 mm), three different flow patterns, i.e., unidirectional (flow parallel with and perpendicular to the shear direction), bi-directional and radial, were taken into account. Corresponding to rotary shear (with a 0.5o shear angle interval up to 90o), only the radial flow pattern was considered. The particle transport was simulated using the Particle Tracking Method, with the particles motion following the fluid velocity fields during shear, as calculated by FEM. For the unidirectional particle transport, the breakthrough curves were analyzed by fitting to an analytical solution of 1-D advection-dispersion equation. The dispersivity, Péclet number and tracer velocity, as well as their evolutions during shear, were determined numerically.</p><p>The results show that the fracture aperture increases anisotropically during translational shear, with a more pronounced increase in the direction perpendicular to the shear displacement, causing significant fluid flow channelling. A more significant increase of flow rate and decrease in travel time of the particles in the direction perpendicular to the shear direction is predicted. The particle travel time and characteristics are, correspondingly, much different when such effects caused by shear are included. This finding may have an important impact on the interpretation of the results of coupled hydro-mechanical and tracer experiments for measurements of hydraulic properties of rock fractures, because hydraulic properties are usually calculated from flow test results along the shear directions, with the effects of the significant anisotropic flow perpendicular to the shear direction ignored. The results also show that safety assessment of a nuclear repository, without considering the effects of stress/deformation of rocks on fluid flow and transport processes, may have significant risk potential. The results obtained from numerical simulations show that fluid flow through a single rough fracture changes with increasing sample size, indicating that representativehydro-mechanical properties of the fractures in the field can only be accurately determined using samples of representative sizes beyond their stationarity thresholds.</p>